This invention relates to rotating seals for continuous flow type centrifuges.
Continuous flow centrifuges provide a continuous flow of fluid into and out of a spinning rotor. This is accomplished by the use of rotating face seals having a rotating member and a nonrotating member in face-to-face contact. While simple in theory, many problems have been encountered with the rotating seals because of their tendency to leak particularly at high speeds. The causes of these leaks are manifold. For one, the rotating member, being connected to the centrifuge rotor, causes the nonrotating member to toss resulting in a separation of the members and leakage at the seal. Such leakage also is caused by misalignment induced vibrations between the faces of the two members and the inability of the two members to track the motion of each other. Additional pressure between the members does not always help. If too much pressure is applied there is undue wear of the seal faces and consequent leakage of the seal.
A number of efforts have been made in the prior art to correct these problems. Thus Jacobson et al. in U.S. Pat. No. 3,443,747 propose the use of a rotating member made of a very hard material with the stationary member being contructed of a tetrafluoroethylene polymer and being vertically movable to accommodate some movement of the rotating element. German Auslegundschrift No. 1,910,576 teaches the use of the seal members made respectively of titanium and fiberglass reinforced plastic. Since both materials have about the same thermal coefficience of expansion alignment problems are reduced. The stationary member is spring loaded against a horizontally movable plate to facilitate its accommodating the transverse movements of the rotary member.
British Pat. No. 925,677 describes a stationary member which is spring loaded against a rotating member, the rotating member being cushion mounted. U.S. Pat. No. 4,011,972, issued to Pederson et al. permits axial movement of the spindle for the stationary seal. Dilks in U.S. Pat. No. 4,357,235 uses a flexible shaft to drive the rotating member. Both members of the seal are mounted on a gasket to facilitate their accommodating the motion of one another. Finally, Romanauskas in his U.S. Pat. No. 4,375,871 positions the rotating seal at the center of mass of the rotor to reduce its vibration and uses a three point spring mounting for the stationary member.
All of these efforts of the prior art have tended to reduce the leakage through the rotating seals of continuous flow centrifuges, many to a significant extent. Many of these approaches, however, tend to encounter difficulty and leak as the rotating speed of the centrifuge is increased above 10,000 rpm. Another problem encountered when the centrifuge is to be used in sedimentation field flow fractionation applications is that it is difficult to maintain alignment of the small diameter flow channels required. The channels must remain relatively small to prevent band broadening in the separation.